This project will look for potential markers that may determine salt-sensitivity and human hypertension. These markers may identify persons at risk to develop hypertension, a better understanding of the pathophysiology of this leading cause of morbidity and mortality in this country, especially in the Black community; and potentially lead to therapeutic strategies to better treat or prevent this disease. After a 1-4 week washout of antihypertensives medications, patients are randomized to either a low salt diet (<30 meq Na/24 hours) or a high salt diet (>200 meq/24 hours). Prepared foods are provided from the CRC kitchen and patients' compliance is assessed in eating the provided foods to achieve required sodium balance. The patients are admitted for an overnight hospital stay during which their sleep breathing patterns are recorded. The next morning, blood pressure measurements are taken every 15 minutes for four hours and blood and urine samples are collected for assay. Subjects then enter the alternate salt phase for the next week and measurements are repeated. To date, 172 participants have completed the study, 59 in the past year. Since the start of the protocol, 172 participants have been completed. Enrollment for this study is scheduled to end early in 1999. A total of 275 participants were screened and most were ineligible for participation due to height/weight restrictions and need for antihypertensive medications.